Since little information is available on the biochemistry of the connective tissues of the periodontium, this laboratory has endeavored to perform studies on the proteins of gingivae, periodontal ligament and cementum. Experiments on human and bovine gingival tissue have indicated that the collagen of this tissue is comprised mainly of molecules with the chain structures (alpha 1(I))2 alpha 2 (Type I collagen). Evidence for a smaller level of Type III collagen was also noted. Likewise, the bovine periodontal ligament appears to contain both Type I and Type III collagens. In contrast, bovine cementum contains almost exclusively collagen with the chain structure (alpha l (I))2alpha2. A significant proportion of the proteins of gingival tissue and of the periodontal ligament is noncollagenous. The aim of this research is to definitely characterize the proteins of the three tissues by techniques previously applied by us and other workers to the study of collagen and noncollagenous proteins of other connective tissues.